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authorMauro Carvalho Chehab <mchehab+samsung@kernel.org>2019-06-18 12:40:23 -0300
committerMauro Carvalho Chehab <mchehab+samsung@kernel.org>2019-07-15 11:03:01 -0300
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parent159a5e78bdcabb1f87ee5536182a99a307ae0bac (diff)
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docs: device-mapper: move it to the admin-guide
The DM support describes lots of aspects related to mapped disk partitions from the userspace PoV. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
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-=========
-dm-flakey
-=========
-
-This target is the same as the linear target except that it exhibits
-unreliable behaviour periodically. It's been found useful in simulating
-failing devices for testing purposes.
-
-Starting from the time the table is loaded, the device is available for
-<up interval> seconds, then exhibits unreliable behaviour for <down
-interval> seconds, and then this cycle repeats.
-
-Also, consider using this in combination with the dm-delay target too,
-which can delay reads and writes and/or send them to different
-underlying devices.
-
-Table parameters
-----------------
-
-::
-
- <dev path> <offset> <up interval> <down interval> \
- [<num_features> [<feature arguments>]]
-
-Mandatory parameters:
-
- <dev path>:
- Full pathname to the underlying block-device, or a
- "major:minor" device-number.
- <offset>:
- Starting sector within the device.
- <up interval>:
- Number of seconds device is available.
- <down interval>:
- Number of seconds device returns errors.
-
-Optional feature parameters:
-
- If no feature parameters are present, during the periods of
- unreliability, all I/O returns errors.
-
- drop_writes:
- All write I/O is silently ignored.
- Read I/O is handled correctly.
-
- error_writes:
- All write I/O is failed with an error signalled.
- Read I/O is handled correctly.
-
- corrupt_bio_byte <Nth_byte> <direction> <value> <flags>:
- During <down interval>, replace <Nth_byte> of the data of
- each matching bio with <value>.
-
- <Nth_byte>:
- The offset of the byte to replace.
- Counting starts at 1, to replace the first byte.
- <direction>:
- Either 'r' to corrupt reads or 'w' to corrupt writes.
- 'w' is incompatible with drop_writes.
- <value>:
- The value (from 0-255) to write.
- <flags>:
- Perform the replacement only if bio->bi_opf has all the
- selected flags set.
-
-Examples:
-
-Replaces the 32nd byte of READ bios with the value 1::
-
- corrupt_bio_byte 32 r 1 0
-
-Replaces the 224th byte of REQ_META (=32) bios with the value 0::
-
- corrupt_bio_byte 224 w 0 32